Triple-pronged ground improvement tool and deployment array

ABSTRACT

A method is given which it is believed will lead to better ground treatment results for both engineering and environmental purposes. The novel advancement over conventional equipment and machines (called pokers) suggested herein is that rather than simply deploying a single ground improvement poker at a time, a triangular array of three pokers, deployed from a single mobile carrier, be activated in the ground together and simultaneously at a particular location. Considerable synergetic advantages are anticipated not only by the mutual interaction of multiple machines in close proximity, but also by the ability to excite the three individual pokers at different frequencies and/or phase relationships with respect to their partners. In the special case of the equipment previously disclosed in U.S. Pat. No. 6,554,543 further enhancements in ground improvements are anticipated by assiduously selecting the pressures at which water or fluids are pumped into or out of the three individual prongs of the composite array of cooperating hydrodynamically assisted vibrators. A deployment pattern devised for this particular triple-pronged tool is given which will allow full and efficient contiguous coverage of any area requiring treatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent application No. 61/260,625 filed Nov. 12, 2009, the disclosure of which is incorporated herein by reference.

The apparatus and method described herein are believed to constitute a substantial improvement over those currently in use by that branch of the Civil Engineering construction industry referred to as Ground Improvement. There are two separate and necessarily complementary ideas/concepts presented. One is the novelty of employing a set of three individual ground improvement machines, structurally interconnected in a triangular configuration to become a single composite tool, such that this new three-pronged composite machine can be mounted on, and supported by, a single deployment conveyance in a manner to allow their simultaneous insertion into (and subsequent withdrawal from) the ground. The other novel aspect of this disclosure is the array pattern for the use of the triple arrangement of machines so as to completely cover a plot of ground in a contiguous manner. The array currently used is shown in one sketch. The novel array found to solve the deployment problem of the new apparatus is shown in another.

METHODS CURRENTLY BEING USED

In order to improve the engineering characteristics (the geotechnical parametric values) of the ground underlying a building site prior to construction, specialist contractors referred to as Ground Improvement [hereinafter abbreviated to “GI”] contractors, operate on the ground using one or other of a variety of pieces of equipment specifically designed and built for this purpose. In many cases the GI contractor will select a machine which consists of a long cylindrical (pipe-like) tool such as the Vibroflot which has been in use since the 1930s. This long tool is sometimes referred to as a poker because of its shape and its use of agitation to improve the situation.

To treat the subject ground and improve its consistency to the depth required by the design engineer, the poker is inserted to an appropriate depth and then caused to exert forces on the soil around it, and in which it is embedded, while it is being withdrawn from the ground. In most cases the treatment force used is vibratory. In the particular case of equipment described in U.S. Pat. No. 6,554,543 the treatment forces are a combination of vibratory and hydrodynamic.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention are illustrated, merely by way of example, in the accompanying drawings in which:

Sketch 1 depicts the equipment and array pattern commonly used in current practice.

Sketch 2 depicts the equipment and novel apparatus, array pattern, and layout configuration advocated herein.

LIST OF REFERENCE NUMERALS

10 elevation view of typical equipment used in current practice

11 deployment vehicle

12 ground/soil

13 mast/leads

14 vertical drive piston/drum

15 poker head

16 poker

20 plan view of typical equipment used in current practice

30 plan view of ground affected by single poker insertion

31 point of insertion axis

40 plan view of typical equilateral triangular array

50 plan view of “honeycomb” pattern giving full coverage of site

60 elevation view of the equipment and novel apparatus

61 structural harnessing of triple-pronged apparatus

62, 63 and 64 individual pokers of triple-pronged apparatus

70 plan view of the equipment and novel apparatus

80 plan view of ground affected by a single novel deployment

82, 83 and 84 points of insertion axes for triple-pronged apparatus

90 plan view of novel tile elements

100 plan view of the novel pattern of deployment giving full coverage of site

Sketch 1 depicts schematically the following:

Elevation view 10 shows a typical apparatus and setup as currently employed in ground treatment. Deployment vehicle 11 as is used to move and operated the equipment at various positions above the ground or soil 12 to be improved. A mast or leads 13 attached to the deployment vehicle 11 as normally used to facilitate the up and down movements of drive piston or drum 14. Poker head mechanism 15 fixes the poker 16 with its long axis vertical, and also either activates the compaction machine or conveys the required energy to a machine located within the body of the poker 16.

20 is a plan view of the elevation view 10 described above.

Plan view 30 shows the hexagonal area of ground considered to be affected by a single poker insertion, where 31 is the point of insertion in plan view.

Plan view 40 shows the typical equilateral triangular array at which the probe 16 is inserted.

Plan view 50 shows the typical honeycomb pattern which gives full coverage of the area of the site to be treated by inserting the probe 16 at each position 31.

Sketch 2 depicts schematically the following:

Elevation view 60 shows the equipment and novel apparatus proposed herein. The deployment vehicle 11, the ground or soil 12, the mast or leads 13, and drive piston or drum 14 are not necessarily significantly different from those described above in 10 and as used in current practice. This novel method involves structural harnessing 61 of the triple-pronged apparatus to the drive 14. In this case 61 incorporates the functions of head 15 in the typical case, but in addition allows the three individual pokers 62, 63 and 64 of the triple-pronged apparatus to be activated independently of each other.

70 is a plan view of the elevation view 60 described above.

Plan view 80 shows the composite area of ground considered to be affected by one application of the triple-pronged apparatus at a single insertion location, where 82, 83 and 84 are the three prong axes of insertion in plan view.

Plan view 90 shows the two mirror images (shape “V” and shape “A”) of the twelve-sided geometric shape shown in 80.

Plan view 100 shows the novel tiled pattern giving full coverage of that part of a site requiring treatment.

DESCRIPTION OF APPARATUS

The novelty of this apparatus is that three separate treatment machines are structurally fixed/harnessed together so that their long axes are vertical and are spaced apart in an equilateral configuration. The composite structure is such that this novel apparatus may be hoisted and lowered by a single deployment vehicle. This mobile carrier provides the power source for all three machines and is designed to activate each of the machines differently and independently. This new composite GI machine is hereinafter referred to as a triple-pronged poker or apparatus and its outline is shown in Sketch 2.

IMPROVEMENTS PROPOSED HEREIN

There are two different approaches to realize advantage from this proposed apparatus and method. The first and most obvious is that the GI contractor need only allocate a single vehicle of deployment (usually a crane or a backhoe rigged with leads), and one team of manpower to an equipment set-up which will yield three times the usual output in the same amount of time. This option seems sufficiently obvious that it requires no further comment/explanation. A second set of opportunities opened by this triple-pronged machine involve miniaturization and synergistic effects, and these are outlined below.

It may be decided that, rather than simply achieving greater productivity, to instead avail of the physical/mechanical benefits accruing from a certain amount of miniaturization. One particular case would be where it was decided to treat with the triple-pronged apparatus the same area per deployment as would have been treated by a single poker working at its optimal array spacing. Referring to the optimal design spacing of a single poker as “SD”, and “TD” to designate the linear separation between the individual machines of the triple-poker apparatus, the dimension TD would in this case equal SD divided by the square root of 3. Naturally, any other spacing in between, which was found/deemed by the geotechnical designer, and/or the project management to be advantageous for the development of a specific site could be chosen. In the case of TD=0.58× SD suggested above there would be no areal advantage at each deployment location, but rather, a different set of mechanical and functional advantages not available to any conventional single poker now available. Some of these advantages are expressed herein below.

For a given ground area to be treated, it seems obvious that the ground excitation effort emanating from each one of the pokers of the three-pronged apparatus need not be as great as that produced by a single poker acting alone in isolation. Therefore it seems justifiable, prior to field verification, to act on that idea, taking it for granted that some size reduction is justifiable in comparison with the single poker dimensions. Reduced size has the obvious benefit of making it easier to physically handle the pokers during shipping, assembly, and maintenance. But more importantly from a geotechnical point of view, pokers of lesser diameter will have greater axial flexibility because of their reduced structural rigidity, thus facilitating impact on the ground of greater horizontal displacement amplitude. Lateral displacement is the real measure of a machine's ability to improve the ground's competency.

A critical dimension, perhaps the most influential one, is the distance from the locus of emanation of the improvement force to the centroid of that part of the soil column being treated. Since high frequency energy is attenuated more rapidly with distance of shock wave travel than are lower frequency vibrations, normal practice has been to build heavy machines running at low frequencies. In this case, where pokers are closer to the centroid of the soil being treated, higher frequencies can be used. The benefit to employing higher frequencies is that the vibratory force generated by a given size machine increases with the square of the frequency at which the eccentric weight is rotated.

The mere fact that there are three independently excitable/empowered tools in the ground at the same time and in dose proximity opens a whole new prospect in ground improvement technology. This is because each of the three neighbouring machines can be made to perform their functions independently, leading to many combinations of forces/influences being available to the design engineer. For instance, the vibrations emitted from each individual poker could be changed in frequency and/or phase relationship with the others. In the particular case of the GI equipment described in U.S. Pat. No. 6,554,543 where both vibratory and hydrodynamic forces are employed, the possibilities to garner the benefits of handshaking between complementary energy sources which are working close enough to one another to produce synergetic effects are simply uncharted.

Again, in the case of U.S. Pat. No. 6,554,543 there is significantly increased potential for environmental enhancement of soils by virtue of having three tools at depth within the ground at the same time. Water could be either pumped into, or sucked out of, the ground by each poker either in tune with its partners, or in a cooperative manner such as to create a flow in any lateral direction between them. In comparison, having one pumped well working alone in isolation may be viewed as somewhat impotent.

HOW THE METHOD WOULD WORK IN PRACTICE

The physical/mechanical operational procedures involved in deploying the hardware, of inserting the composite machine in the ground, and then improving the ground while it is being withdrawn, remain essentially the same as are currently employed with conventional GI equipment of this type.

The opportunity for differential manipulation of the excitation energies of the three separate sources is of course new, and how to take best advantage of this novel aspect of the three-pronged poker would be left to the geotechnical designer to specify/determine on a case-by-case basis.

The key to being able to avail of, or have access to, the benefits attributable to, and inherent in, this composite poker is finding an array pattern by which to deploy it in a manner which could cover the whole area needing treatment without significant wasted effort, or double/overlapping treatment. Basically, although a technically superior instrument/machine, it would have limited practicality/application if it were not for finding a simple geometric pattern/solution over which to deploy it in an acceptably practical manner. Such an array was devised and is shown in Sketch 2.

Here it is taken/understood that the extent of ground affected by the three-pronged machine is the same ground as would have been affected had three separate machines been deployed at the same separation as the prongs on the triple apparatus. This leads to a composite shape as is labelled “V” in the sketch. The solution to fitting elemental shapes of this rather complex 12-sided geometric shape together so as to most efficiently cover an expanse of ground without leaving areas untreated was found as follows. A second elemental shape, called “A”, was created by a vertical inversion of “V”. These two shapes in combination were found capable of fully covering any ground surface area shape. This simple method is depicted in Sketch 2.

In addition to its value as a tool for improving the engineering properties of a site, and in the particular case of U.S. Pat. No. 6,554,543 its environmental quality, there is the following specific application. The soil within the compass of the three separate prongs can be made into a very dense column which could replace the “stone-column” approach (which attempts to provide foundation support and liquefaction treatment), and here, without the need to import crushed rock. 

1. A method of ground improvement using three separate machines (pokers) held together in a triangular array which are deployed by a single mobile carrier and having the control to activate the three pokers either in unison or independently with respect to vibration frequency and amplitude.
 2. A method of ground improvement using three separate machines (pokers) of the U.S. Pat. No. 6,554,543 design held together in a triangular array which are deployed by a single mobile carrier and having the control to activate the three pokers either in unison or independently with respect to vibration frequency and amplitude and/or also the pressures at which water or fluid is pumped into or out of the ground surrounding each poker.
 3. A method whereby any area of ground can be fully and efficiently treated with a triangular array of pokers by adopting as the unit of treatment a particular 12-sided geometric shape which is arranged in a contiguous pattern of rows and where alternating rows have the orientation of the shape inverted with respect to adjacent rows. 